It sits perfectly well with me if people choose to be career First Officers, provided that he/she never forgets that he/she is the Deputy Commander of the aircraft, and should be mentally prepared and confident to assume the Command role due to circumstance or situation.
Over the years there have been a sufficient number of F/Os achieving "Instant Command" due to the Captain's incapacitation or death to warrant this assertion.
If they feel competent to command, then it's fine with me. If not, perhaps they should seek an alternative form of employment.
Best Regards,
Old Smokey